1. Field of the Invention
Aspects of the present invention relate to a duplex document scanning method and an apparatus for sequentially reading images from both sides of a document, and more particularly, to a duplex document scanning method and apparatus for scanning both sides of a duplex document quickly.
2. Description of the Related Art
In conventional duplex document scanning apparatuses, a duplex document is automatically fed and images are read from both sides of the duplex document. Such conventional duplex document scanning apparatuses are widely used for various image reading/processing devices such as scanners, copiers, fax machines, and multifunctional apparatuses.
FIGS. 1A through 1E are views for illustrating an example of a conventional duplex document scanning apparatus and its scanning method disclosed in U.S. Pat. No. 5,430,536 to Fullerton et al. Referring to FIG. 1A, a document sheet D is picked up from a document input tray 20 and is fed along a document feed path. Moving to FIG. 1B, an image is read from one side of the document sheet D by a reader 14. Then, the document sheet D is delivered onto a document output tray 22 by eject rollers 50. If the document sheet D is single sided (i.e., the document sheet D is a simplex sheet), the eject rollers 50 completely eject the simplex document sheet D onto the document output tray 22. However, if the document sheet D is double sided (i.e., the document sheet D is a duplex sheet), the eject rollers 50 are reversely rotated before the duplex document sheet D is fully ejected so that the other side of the duplex document sheet D may be read by the reader 14 as shown in FIG. 1C. In this case, a back edge of the duplex document sheet D passes by the reader 14 first. As such, the duplex document sheet D can be fed again along the document feed path so that an image from the other side of the duplex document sheet D may be read. Referring to FIG. 1D, when the duplex document sheet D passes by the reader 14 again, the other side of the duplex document sheet D faces the reader 14, and thus, the other side of the duplex document sheet D can be scanned. In this way, images can be read automatically and sequentially from both sides of the duplex document sheet D.
However, if the duplex document sheets D are directly ejected onto the document output tray 22 after both sides of the duplex document sheets D have been scanned, the duplex document sheets D may be stacked on the document output tray 22 in a reverse order when compared to the order in which the duplex document sheets D were initially stacked on the document input tray 20. In other words, in the case of scanning simplex document sheets D, the simplex document sheets D are stacked on the document input tray 20 with front sides of the simplex document sheets D facing up. After scanning one side of the simplex document sheets, the simplex document sheets D are sequentially stacked on the document output tray 22 with the front sides of the simplex document sheets D facing down. Therefore, the simplex document sheets D are stacked in the same initial order as that of when the simplex document sheets D were initially stacked on the document input tray 20 but the simplex document sheets D are upside-down. However, after scanning duplex document sheets D, the duplex document sheets D are stacked on the document output tray 22 with the front sides of the duplex document sheets D facing up since the duplex document sheets D pass by the reader 14 two times as described above. As a result, the stacked order of the duplex document sheets D is reversed after scanning both of the sides, and thus, it is very inconvenient to rearrange the duplex document sheets D in the order in which the duplex document sheets D were initially stacked on the document input tray 20. To stack the duplex document sheets D in the order in which the duplex document sheets D were stacked on the document input tray 20, after scanning both sides of each duplex document sheet D, each duplex document sheet D is fed along the document feed passage one more time as shown in FIG. 1E. Hence, after scanning both sides of each duplex document sheet D, the duplex document sheet D is fed back by the reverse rotation of the eject rollers 50 back into the document feed path across the reader 14 one more time to reverse the duplex document sheet D, and then, the duplex document sheet D is ejected onto the document output tray 22. In this way, the duplex document sheets D are stacked on the document output tray 22 in the same initial stack order that the duplex document sheets D were stacked on the document input tray 20.
However, when the duplex document sheets D have been scanned in this way, it takes substantial time to scan and stack the duplex document sheets D in the correct order as each of the duplex document sheets D must pass by the reader 14 three times. Hence, after a duplex document sheet D passes by the reader 14 three times (two times for scanning and one time for stack-order arrangement), the next duplex document sheet D can be fed, which increases the time required for scanning the duplex document sheets D. Although the increase of scanning time is negligible when one or two duplex document sheets D are scanned, the increase in scanning time cannot be neglected when tens to several hundreds of duplex document sheets D need scanning.